Maintenance & Technical > KX500 Original

1990 pro circuit pipe?

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Fookeneh:
I have this on my 94, with a rad valve and a spark arrester silencer.Not sure how the carb is set up. It pulls seamlessly through the revs,but it flattens out and makes my hands numb with vibes at full throttle. Does anyone have experience with this pipe? I think it might be for mid range.

mikesmith:
They make 2 differnt pipes,MX or Desert.I run the MX pipe and it smooths out the bike a little compared to the stock pipe,but it does pull on top.The vibration is probally your crank being out of true,a pretty common thing on a 500 and maybe you need to work on your jetting if its not pulling on top.But if its vibrating bad and its not because your trying to ride it like a 125 or it has a broken motor mount or something (is this your first 500,because compared to other bikes the do vibrate),I would check your crank bearings.They may be worn or if someone has reved it a lot with a untrue crank it can oval out the cases where the bearings mount.

FastKX500:
I have a pro circuit platnium pipe on my 90 500, and yea it does vibrate alot..So now I gues its the pipe?

Fookeneh:
I rode an  84 cr 500 when I was 16 (16 years ago) and ya ,it vibrated alot too.Its the nature of the beast. Maybey this winter I'll split the cases on the k5 and get the crank trued. It would feel like a different machine if even half of the vibes went away.It doesn't pull hard on the top end but it kinda feels like the motor is saying to me " Do we really have to rev this high ?" The torque is awesome...I short shift everywhere,so I really only rev it up when I feel like being a yahoo in 5th gear. The motor is hard on sprockets and swing arm bearings ,but that is the price I pay for riding a man's bike. The pipe has nothing to do with the vibrations and I really think nothing is out of the ordinary.I will tear the motor down before I hit the Oregon dunes so I can make her run as smooth as possible on the top end.

Twist-a-grip:
Big bore 2-strokes do vibrate more than smaller engines.  ANY of them will vibrate badly if:
1. worn/loose crank bearings
2. loose motor/head mounts
3. bent or otherwise untrue crank
4. The exhaust MUST be securely mounted!(remember the pipe is an extension of the motor)
The latter is the most common and easy to fix.  I have ridden 250's that vibrated so bad because of this that I couldn't stand riding them.  Any broken or loose mounting hardware on the pipe will make it vibrate more than it should.
If what you have is normal vibration then there are parts and tricks to lessen the vibration.  Paul is dead on about the Pro Taper bars.  I filled mine about 6"in with silicone and added FMF ergo grips for additional vibration prevention and I barely notice it. I feel more in my legs than arms.
John

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